There are a number of automatic air brake systems in the prior art teachings. One of these previous systems is exemplified in the present application and is shown and disclosed in NABUKO GIHOO No. 63, pages 50 and 51, published January, 1987. This example of the prior art system will be explained hereinafter by reference to FIGS. 7 and 8 of the drawings of the present application.
Referring now to FIG. 7 of the drawings, there is shown a brake control system in which normal braking is achieved and is illustrated in the graphic representation of FIG. 8.
At time t.sub.1, the brake valve BV3 is moved into overlapped position after the normal brake operation. This causes a conditioning signal S which is equal to zero (0) to be conveyed to the controller CB3 by the brake valve BV3. At the same time, the balance air reservoir ER is depressurized by a selected amount, namely, by 2.0 Kg/cm.sup.2, reduction occurs so that its pressure remains at 3.0 Kg/cm.sup.2.
In addition, the early charging switch SW is in an OFF position so that the electrical controller CB3 switches the first electromagnetic valve MV1 to its OFF position. Thus, the valve MV1 assumes its exhause position . At the same time, the second electromagnetic valve MV2, for closing the brake line BP, is turned OFF and assumes its closed position .
As shown in FIG. 7, a first pilot chamber A1 of a relay valve RV3 is connected to the balance air reservoir ER, and the pressure is reduced by a selected amount. The relay valve RV3 includes a second pilot chamber A2 for early charging which is opened to atmosphere via the first electromagnetic valve MV1. Thus, the relay valve RV3 is in the overlapped position, which vents the output chamber B by a selected amount and keeps it at that pressure. In this overlapped state, the air supply valve D is seated on hollow exhaust valve rod C and also is seated on air supply valve seat E. Thus, the output chamber B and the exhaust chamber G are blocked off from the air supply chamber F. Accordingly, the up and down forces on the balance piston diaphragm H are balanced, as viewed in FIG. 7.
It will be appreciated that during a normal braking operation the brake line BP is decreased by a selected amount of pressure. Before braking, the brake line is maintained at a normal pressure level due to the second electromagnetic valve MV2 being in an ON or open position. It will be noted that the brake control valve CV on the lead unit or locomotive and the brake control valves (not shown) on the trailing railway vehicles or freight cars revert to an overlapped state after the braking operation. The pressure in the brake cylinder BC of each railway vehicle or freight car is maintained at the pressure corresponding to the normal brake command signal.
Under normal running conditions, the brake valve BV3 is switched into the normal brake position so that the balance air reservoir ER begins to be pressurized. The pressure in this balance air reservoir ER is conveyed into the controller CB3 via line ERP.
At the same time, when the early charging switch SW is turned ON, the controller CB3 switches the first electromagnetic valve MV1 to an ON condition so that it is shifted to the air supply position .quadrature.. Simultaneously, the second electromagnetic valve MV2 is turned ON and switches to its open position =.
Therefore, the first pilot chamber A1 of the relay valve RV3 is pressurized by the above-mentioned balance air reservoir ER, while the second pilot chamber A2 is pressurized by the high pressure air in the main air reservoir line MRP via the first electromagnetic valve MV1. The balance piston diaphragm H and the supplemental piston diaphragm I cause the exhaust valve rod C to move upward as viewed in FIG. 7 so that the air supply valve D becomes unseated from the air supply valve seat E. This is called air supply exhaust operation.
Therefore, the air is supplied to the brake line BP by the main air reservoir line MRP via the air supply chamber F and the output chamber B of the relay valve RV3 and via the open position = of the second electromagnetic valve MV2. Thus, the pressure in the brake line BP quickly rises.
This pressure in the brake line BP is conveyed to the electrical controller CB3 via line BP1 as well as by line BP2 via the throttle valve NV2 and the buffer or cushion air reservoir VR, as shown in FIG. 8. Thus, the pressure in the brake line BP1 is equal to the pressure in the brake line BP of the lead unit or locomotive, and the pressure in the brake line BP2 is equal to the pressure in the supplemental air reservoir AR of the first connected railway vehicle or freight car.
When the pressure in the brake line BP1 exceeds a first predetermined pressure, such as 4.9 Kg/cm.sup.2, the controller CB3 causes the second electromagnetic valve MV2 to switch OFF to its closed position .
Subsequently, when the pressure in the brake line BP1 falls below a first predetermined pressure, the electrical controller CB3 again causes the second electromagnetic valve MV2 to switch ON to its opened position =. The electromagnetic valve MV2 remains in this opened position = for a first predetermined period of time, such as, 0.5 seconds as shown in FIG. 7. When the first predetermined time has expired, the second electromagnetic valve MV2 switches to an OFF condition. Moreover, even if the pressure in the brake line BP1 does not decrease to the above-mentioned first predetermined pressure, the second electromagnetic valve MV2 passes a second predetermined time, such as 2.0 seconds so that after it is turned OFF, while brake line BP2 is less than a second predetermined pressure, such as 4.8 Kg/cm.sup.2, the second electromagnetic valve MV2 will switch back to its ON condition.
Thus, the pressure build-up in the brake line BP continues until the brake line BP2 reaches the above-mentioned second predetermined pressure of 4.8 Kg/cm.sup.2.
When the brake line BPZ reaches the second predetermined pressure, the controller CB3 switches the first electromagnetic valve MV1 to an OFF condition so that it returns to its exhaust position . Thus, the relay valve RV3 returns to the normal release operation so that the second pilot chamber A2 is opened to atmosphere.
Now, when the pressure in the output chamber B and in brake line BP1 balances the pressure in the balance air reservoir ER and in line ERP, which is regulated to a specified pressure, namely 5.0 Kg/cm.sup.2, the relay valve RV3 returns to an overlapped state.
At the same time, the brake line BP is pressurized to a specified pressure so that the brake control valve CV is switched to its exhaust position and supplements the supplemental air reservoir AR up to a selected pressure. Simultaneously, the brake control valve CV opens the brake cylinder BC to atmosphere.
Under this condition, the brakes are released and the brake valve BV3 is returned to the normal brake position. The balance air reservoir ER is exhausted by a selected amount. Simultaneously, the first pilot chamber A1 is also exhausted so that the exhaust valve rod C in the relay valve RV3 moves downwardly as shown in FIG. 7 so that it opens hollow rod C and exhausts the output chamber B. This is called exhaust operation.
When the brake valve BV3 is in normal braking operation, the status signal S is equal to one (1). Therefore, the controller CB3 switches the second electromagnetic valve MV2 to an ON condition, so that it assumes an opened position =.
Therefore, the brake line BP is connected to the output chamber B through the opened position = of the second electromagnetic valve MV2. Correspondingly, the brake control valve CV of each car controls the braking operation.
When the exhaustion of the brake line BP reaches a specified amount, the relay valve RV3 returns to the overlap state, as shown in FIG. 7. At the same time, the controller CB3 switches the second electromagnetic valve MV2 to its OFF condition so that it assumes the closed position .
In the prior art system, as described above, the repeated operation of the second electromagnetic valve MV2 for opening and closing the brake line BP is excessive so that wear and failure is likely to occur. It is obvious that this is a serious problem.
In addition, in a short train, in which the number of connected railway vehicles or freight cars is relatively small, the early charging control is accomplished by the operation of the early charge switch SW. Accordingly, the brake lines BP of all of the railway vehicles or freight cars will be over-charged to a pressure which is more than the selected minimum pressure. This is another disadvantage.
In other words, the first problem, described above, results from the fact that the second electromagnetic valve MV2 repeatedly switches between its ON and OFF positions during the period from the START of the early charge control to the END, as shown in FIG. 8 so that its cycle is very short.
The second problem, described above, results from the fact that the pressure BP1 in the brake line BP of the lead unit or locomotive and the pressure BP2 in the supplemental air reservoir AR of the first railway vehicles or freight cars, are effected by the setting of the throttle valve NV2 and the buffer air reservoir VR. This is used to switch the first electromagnetic valve MV1 and the second electromagnetic valve MV2 between their ON and OFF positions during the early charge control. In particular, the pressure build-up rate of the brake line BP2 is based on the throttling effect of the throttle valve NV2 and the capacity of the buffer air reservoir VR which are set so that the early charge control works more effectively in proportion to the brake line BP capacity of a long train in which the number of connected railway vehicles or freight cars is relatively large. Thus, in the case of a short train, if the brake line BP of all of the connected railway vehicles or freight cars is greater than a selected pressure, the brake line will not exceed the above-mentioned second predetermined pressure of 4.8 Kg/cm.sup.2 so that the early control operation is continued.